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Tl Posts:

Posted - 4/28/2002 4:44:30 PM  Show Profile  Email Poster  Edit Message
I think many people are misunderstanding the use of commas, and it's creating more problems than solutions. As far as I see, commas only have one purpose.

Many Conexant and PCTel modems are dualmode Flex and V.90. When dialing a Flex-only server, the modem will use flex (duh). When dialing a V.90-only or V90/X2 server, the modem would correctly use V.90. However, when it's dialing to a Flex/V.90 server, Conexant modems tend to negotiate K56Flex, and PCTel modems do some combination of both (ie. The handshake is IDENTICAL to the flex handshake, except the DIL sequence is still present.), but the PCTel fails with a double-handshake.

Commas are used to SKIP OVER the Flex signal and drop in on the V.90 signal. when calling Flex/V.90 servers, use 2 to 3 commas AT MOST! When calling V.90/X2 servers, use NO COMMAS. Too many commas will give you either a V.32 (14.4) or ANOTHER Flex connection!!

Tl Posts:

Posted - 4/29/2002 10:28:51 AM  Show Profile  Email Poster  Edit Message  v.Richards Homepage
The info above is not entirely correct.
A comma, by default, causes the modem to pause dialing for (default) 2 seconds, see

It is not correct that a dual-mode V.90/K56Flex modem will connect by default with K56Flex to a V.90/K56Flex server. In most cases, the connection attempt will be V.90 first, then K56Flex and lower protocols. (There is no version of K56Flex handshake that includes a DIL.)

While it is better to control protocol via an init string - - it's possible to effect a difference with comma's which delay the client modem's handshake. In particular, servers capable of K56Flex generally also support V.8bis which are the first tones sent by the server side modem when a call is answered. V.8bis provides a method for the modems to communicate what protocols they support and want to use; if both modems don't support V.8bis, the protocols used are based upon trial/error in the handshake. The right # of commas can prevent V.8bis from being used since it is the first part of the handshake.

It is correct that too many commas can result in low connect rates: if the client modem is still 'dialing' because of commas as the handshake proceeds, the server modem is trying lower and lower speeds.

Aloha! Richard.

Tl Posts:

Posted - 4/29/2002 2:06:35 PM  Show Profile  Email Poster  Edit Message
hmm... My Conexant would only connect in Flex mode to a Flex/V90 server, unless I am misunderstanding the handshake sequence and the connect speed. Ok, here's my best description:




from now, I get the dial tone and the normal dialing. Then after a short pause, I hear two beeps and a series of ringing sounds after that. Then, it sounds like a normal V.34 handshake, only the second half is considerably longer, then there is a short buzzing sound and a beep.



I always thought that both the ringing and the 42k connect are characteristic of a Flex connect. If I add two commas, then the handshake is considerably different, no ringing, and also there is a looooooooong buzzing sequence toward the end. (the DIL?)

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